Numerous equalizer products are available for use with SDI cables or other transmission media for propagating a digital communication signal. For practical and performance reasons, however, the maximum cable length supported by a typical cable equalizer is limited. Further, because a typical cable equalizer performs both linear and non-linear operations, it is usually not feasible to cascade multiple cable equalizers together in order to support longer cable lengths. It is therefore desirable to provide an equalization circuit that may be extended to support increased cable lengths.
In accordance with the teachings described herein, an extended equalizer circuit is provided for equalizing a digital communication signal transmitted over a transmission medium that causes a frequency-dependent attenuation of the digital communication signal. An equalizer may be used that includes a linear equalization circuit that is configured to apply a linear filter to the digital communication signal to compensate for the frequency-dependent attenuation caused by a first portion of the transmission medium. The equalizer may also include a non-linear equalization circuit that is configured to apply one or more non-linear operations to the digital communication signal. A de-emphasizing equalizer circuit may be coupled in series between the transmission medium and the equalizer and configured to apply an additional linear filter to the digital communication signal in order to compensate for the frequency-dependent attenuation caused by a second portion of the transmission medium.
A method for extending an SDI equalizer to equalize greater cable lengths is also provided. The method may include the steps of configuring the SDI equalizer to compensate for frequency-dependent attenuation in a digital communication signal caused by a first portion of a transmission cable, and coupling a de-emphasizing filter in series between the transmission cable and the SDI equalizer. The SDI equalizer is also configured to apply one or more non-linear operations to the digital communication signal. The de-emphasizing filter is configured to compensate for frequency-dependent attenuation in the digital communication signal caused by a second portion of the transmission cable, but does not perform any non-linear operations to the digital communication signal.
A stand-alone equalizer circuit for use in an SDI link is also provided. A de-emphasizing filter may be used to receive a digital communication signal from a transmission cable and to apply a linear filter to the digital communication signal to compensate for frequency-dependent attenuation in the digital communication signal caused by the transmission cable, where the de-emphasizing filter does not apply any non-linear operations to the digital communication signal. An amplifier may be coupled to the de-emphasizing filter and configured to amplify the digital communication signal to compensate for flat attenuation caused by the de-emphasizing filter and the transmission cable.